Images acquired from many imaging devices usually contain noise. This noise can adversely impact the perception of such images and distort the effect of subsequent image processing steps. Many systems can produce signal dependent noise. In medical x-ray imaging, there exists a direct trade-off between patient exposure and image quality. The desire to maintain lower exposure dosages results in more noise present in the image. It is, therefore, beneficial to reduce the amount of noise subsequent to image acquisition.
The present application is related to U.S. Pat. No. 5,091,972, entitled "System and method for Reducing Digital Image Noise", by Kwon et. al. dated Feb 25, 1992. It is also related to U. S. patent application Ser. No. 399,134 filed on Aug. 28, 1989, entitled "Digital Image Noise REduction of Luminance and Chrominance base on Overlapping Planar Approximation", by Kaplan et. al. and U.S. patent application Ser. No. 07/399,135 filed on Aug. 28, 1989, entitled "A Computer Based Digital Image Noise Reduction Method Based on Overlapping Planar Approximation" by Kaplan et. al. The techniques described by Kaplan and Kwon have two major drawbacks which are overcome by the invention presented in this disclosure. The first drawback relates to estimating the precise amount of noise to be expected.in an image. These previous techniques require an a priori estimate of the noise present in the image. In practice, such estimates are derived through laborious calibration and measurement of the particular imaging system used in the application. Our technique estimates the noise on each image input to the system. As such, it is not particular to any particular imaging system. The second drawback relates to the fact that these techniques use a single signal-independent estimate for noise across the entire dynamic range of the image. Our technique differentially estimates and removes noise as a signal-dependent function of image the image features themselves